Multi-Anode Solid Electrolytic Capacitor Assembly

ABSTRACT

A capacitor assembly that is stable under extreme conditions is provided. A capacitor assembly that is capable of achieving a high capacitance and yet remain thermally and mechanically stable under extreme conditions. Even at high capacitance values, good mechanical stability can be achieved by connecting multiple individual capacitor elements to the housing of the assembly. Without intending to be limited by theory, it is believed that the use of multiple elements increases the surface area over which the elements are connected to the housing. Among other things, this allows the elements to dissipate vibrational forces incurred during use over a larger area, which reduces the likelihood of delamination. The capacitor elements are also enclosed and hermetically sealed within a single housing in the presence of a gaseous atmosphere that contains an inert gas, thereby limiting the amount of oxygen and moisture supplied to the solid electrolyte of the capacitor elements. Through the combination of the features noted above, the capacitor assembly is able to better function under extreme conditions.

BACKGROUND OF THE INVENTION

Electrolytic capacitors (e.g., tantalum capacitors) are increasinglybeing used in the design of circuits due to their volumetric efficiency,reliability, and process compatibility. For example, one type ofcapacitor that has been developed is a solid electrolytic capacitor thatincludes an anode (e.g., tantalum), a dielectric oxide film (e.g.,tantalum pentoxide, Ta₂O₅) formed on the anode, a solid electrolytelayer, and a cathode. The solid electrolyte layer may be formed from aconductive polymer, such as described in U.S. Pat. Nos. 5,457,862 toSakata, et al., 5,473,503 to Sakata, et al., 5,729,428 to Sakata, etal., and 5,812,367 to Kudoh, et al. Unfortunately, however, thestability of such solid electrolytes is poor at high temperatures due tothe tendency to transform from a doped to an un-doped state, or viceversa. In response to these and other problems, capacitors have beendeveloped that are hermetically sealed to limit the contact of oxygenwith the conductive polymer during use. U.S. Patent Publication No.2009/0244812 to Rawal, et al., for instance, describes a capacitorassembly that includes a conductive polymer capacitor that is enclosedand hermetically sealed within a ceramic housing in the presence of aninert gas. The housing includes a lid that is welded to the sidewalls ofa base structure. According to Rawal, et al., the ceramic housing limitsthe amount of oxygen and moisture supplied to the conductive polymer sothat it is less likely to oxidize in high temperature environments, thusincreasing the thermal stability of the capacitor assembly.

Despite the benefits achieved, however, problems nevertheless remain.For example, high capacitance applications generally require a largeanode size to achieve the desired capacitance. Due to its large size,however, the capacitor element is mechanically instable, particularlyunder extreme conditions (e.g., high temperature of above about 175° C.and/or high voltage of above about 35 volts), which leads to leading todelamination and poor electrical performance.

As such, a need currently exists for a capacitor that is capable ofachieving a high capacitance and yet remain stable even under extremeconditions.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a capacitorassembly comprising is disclosed. The assembly comprises a housing thatdefines an interior cavity having a gaseous atmosphere that contains aninert gas. The assembly also comprises a first capacitor elementjuxtaposed adjacent to a second capacitor element, wherein the first andsecond capacitor elements are positioned in the interior cavity andconnected to the housing. Each of the capacitor elements comprise ananode formed from an anodically oxidized, sintered porous body and asolid electrolyte overlying the anode. The capacitor elements furthercomprise an anode lead that extends in a lateral direction from theporous body of the anode, wherein the lead is positioned within theinterior cavity of the housing. An anode termination is in electricalconnection with the anode lead of each of the capacitor elements and acathode termination is in electrical connection with the solidelectrolyte of each of the capacitor elements.

Other features and aspects of the present invention are set forth ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth more particularly in the remainder of the specification, whichmakes reference to the appended figures in which:

FIG. 1 is a front view of one embodiment of a capacitor assembly of theassembly of the present invention;

FIG. 2 is a front view of the capacitor assembly of FIG. 1, with the lidand sealing member removed; and

FIG. 3 is a cross-sectional view of the capacitor assembly of FIGS. 1and 2, taken along a line 3-3.

Repeat use of references characters in the present specification anddrawings is intended to represent same or analogous features or elementsof the invention.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentinvention, which broader aspects are embodied in the exemplaryconstruction.

Generally speaking, the present invention is directed to a capacitorassembly that is capable of achieving a high capacitance and yet remainthermally and mechanically stable under extreme conditions. Although thecapacitance value of the assembly may vary depending on the application,it can range from about 200 to about 10,000 μF, in some embodiments fromabout 500 to about 8,000 μF, in some embodiments from about 1,000 toabout 6,000 μF, and in some embodiments, from about 2,000 to about 5,000μF, measured at an operating frequency of 120 Hz and temperature ofabout 23° C.±about 2° C. Even at such high capacitance values, goodmechanical stability can be achieved by connecting multiple individualcapacitor elements to the housing of the assembly. Without intending tobe limited by theory, it is believed that the use of multiple elementsincreases the surface area over which the elements are connected to thehousing. Among other things, this allows the elements to dissipatevibrational forces incurred during use over a larger area, which reducesthe likelihood of delamination. The capacitor elements are also enclosedand hermetically sealed within a single housing in the presence of agaseous atmosphere that contains an inert gas, thereby limiting theamount of oxygen and moisture supplied to the solid electrolyte of thecapacitor elements. Through the combination of the features noted above,the capacitor assembly is able to better function under extremeconditions.

Various embodiments of the present invention will now be described inmore detail.

I. Capacitor Elements

As indicated above, the capacitor assembly includes multiple capacitorsin a juxtaposed relationship. Any number of capacitor elements maygenerally be employed. For example, the capacitor assembly may containfrom 2 to 8 capacitor elements (e.g., 2, 3, or 4), in some embodimentsfrom 2 to 4 capacitor elements, in some embodiments from 2 to 3capacitor elements, and in one particular embodiment, 2 capacitorelements.

Regardless of the number employed, the capacitor element includes ananode. When employed in high voltage applications, it is often desiredthat the anode is formed from a powder having a relatively low specificcharge, such as less than about 70,000 microFarads*Volts per gram(“μF*V/g”), in some embodiments about 2,000 μF*V/g to about 65,000μF*V/g, and in some embodiments, from about 5,000 to about 50,000μF*V/g. Of course, although powders of a low specific charge maysometimes be desired, it is by no means a requirement. Namely, thepowder may also have a relatively high specific charge of about 70,000microFarads*Volts per gram (“μF*V/g”) or more, in some embodiments about80,000 μF*V/g or more, in some embodiments about 90,000 μF*V/g or more,in some embodiments about 100,000 μF*V/g or more, and in someembodiments, from about 120,000 to about 250,000 μF*V/g.

The powder may contain a valve metal (i.e., metal that is capable ofoxidation) or valve metal-based compound, such as tantalum, niobium,aluminum, hafnium, titanium, alloys thereof, oxides thereof, nitridesthereof, and so forth. For example, the valve metal composition maycontain an electrically conductive oxide of niobium, such as niobiumoxide having an atomic ratio of niobium to oxygen of 1:1.0±1.0, in someembodiments 1:1.0±0.3, in some embodiments 1:1.0±0.1, and in someembodiments, 1:1.0±0.05. For example, the niobium oxide may beNbO_(0.7), NbO_(1.0), NbO_(1.1), and NbO₂. Examples of such valve metaloxides are described in U.S. Pat. Nos. 6,322,912 to Fife; 6,391,275 toFife et al.; 6,416,730 to Fife et al.; 6,527,937 to Fife; 6,576,099 toKimmel, et al.; 6,592,740 to Fife, et al.; and 6,639,787 to Kimmel, etal.; and 7,220,397 to Kimmel, et al., as well as U.S. Patent ApplicationPublication Nos. 2005/0019581 to Schnitter; 2005/0103638 to Schnitter,et al.; 2005/0013765 to Thomas, et al., all of which are incorporatedherein in their entirety by reference thereto for all purposes.

The particles of the powder may be flaked, angular, nodular, andmixtures or variations thereof. The particles also typically have ascreen size distribution of at least about 60 mesh, in some embodimentsfrom about 60 to about 325 mesh, and in some embodiments, from about 100to about 200 mesh. Further, the specific surface area is from about 0.1to about 10.0 m²/g, in some embodiments from about 0.5 to about 5.0m²/g, and in some embodiments, from about 1.0 to about 2.0 m²/g. Theterm “specific surface area” refers to the surface area determined bythe physical gas adsorption (B.E.T.) method of Bruanauer, Emmet, andTeller, Journal of American Chemical Society, Vol. 60, 1938, p. 309,with nitrogen as the adsorption gas. Likewise, the bulk (or Scott)density is typically from about 0.1 to about 5.0 g/cm³, in someembodiments from about 0.2 to about 4.0 g/cm³, and in some embodiments,from about 0.5 to about 3.0 g/cm³.

Other components may be added to the powder to facilitate theconstruction of the anode body. For example, a binder and/or lubricantmay be employed to ensure that the particles adequately adhere to eachother when pressed to form the anode body. Suitable binders may includecamphor, stearic and other soapy fatty acids, Carbowax (Union Carbide),Glyptal (General Electric), polyvinyl alcohols, naphthalene, vegetablewax, and microwaxes (purified paraffins). The binder may be dissolvedand dispersed in a solvent. Exemplary solvents may include water,alcohols, and so forth. When utilized, the percentage of binders and/orlubricants may vary from about 0.1% to about 8% by weight of the totalmass. It should be understood, however, that binders and lubricants arenot required in the present invention.

The resulting powder may be compacted using any conventional powderpress mold. For example, the press mold may be a single stationcompaction press using a die and one or multiple punches. Alternatively,anvil-type compaction press molds may be used that use only a die andsingle lower punch. Single station compaction press molds are availablein several basic types, such as cam, toggle/knuckle and eccentric/crankpresses with varying capabilities, such as single action, double action,floating die, movable platen, opposed ram, screw, impact, hot pressing,coining or sizing. After compaction, the resulting anode body may thenbe diced into any desired shape, such as square, rectangle, circle,oval, triangle, hexagon, octagon, heptagon, pentagon, etc. The anodebody may also have a “fluted” shape in that it contains one or morefurrows, grooves, depressions, or indentations to increase the surfaceto volume ratio to minimize ESR and extend the frequency response of thecapacitance. The anode body may then be subjected to a heating step inwhich most, if not all, of any binder/lubricant are removed. Forexample, the anode body is typically heated by an oven that operates ata temperature of from about 150° C. to about 500° C. Alternatively, thebinder/lubricant may also be removed by contacting the pellet with anaqueous solution, such as described in U.S. Pat. No. 6,197,252 toBishop, et al.

Once formed, the anode body is then sintered. The temperature,atmosphere, and time of the sintering may depend on a variety offactors, such as the type of anode, the size of the anode, etc.Typically, sintering occurs at a temperature of from about from about800° C. to about 1900° C., in some embodiments from about 1000° C. toabout 1500° C., and in some embodiments, from about 1100° C. to about1400° C., for a time of from about 5 minutes to about 100 minutes, andin some embodiments, from about 30 minutes to about 60 minutes. Ifdesired, sintering may occur in an atmosphere that limits the transferof oxygen atoms to the anode. For example, sintering may occur in areducing atmosphere, such as in a vacuum, inert gas, hydrogen, etc. Thereducing atmosphere may be at a pressure of from about 10 Torr to about2000 Torr, in some embodiments from about 100 Torr to about 1000 Torr,and in some embodiments, from about 100 Torr to about 930 Torr. Mixturesof hydrogen and other gases (e.g., argon or nitrogen) may also beemployed.

An anode lead may also be connected to the anode body that extends in alateral direction therefrom. The anode lead may be in the form of awire, sheet, etc., and may be formed from a valve metal compound, suchas tantalum, niobium, niobium oxide, etc. Connection of the lead may beaccomplished using known techniques, such as by welding the lead to thebody or embedding it within the anode body during formation (e.g., priorto compaction and/or sintering).

The anode is also coated with a dielectric. The dielectric may be formedby anodically oxidizing (“anodizing”) the sintered anode so that adielectric layer is formed over and/or within the anode. For example, atantalum (Ta) anode may be anodized to tantalum pentoxide (Ta₂O₅).Typically, anodization is performed by initially applying a solution tothe anode, such as by dipping anode into the electrolyte. A solvent isgenerally employed, such as water (e.g., deionized water). To enhanceionic conductivity, a compound may be employed that is capable ofdissociating in the solvent to form ions. Examples of such compoundsinclude, for instance, acids, such as described below with respect tothe electrolyte. For example, an acid (e.g., phosphoric acid) mayconstitute from about 0.01 wt. % to about 5 wt. %, in some embodimentsfrom about 0.05 wt. % to about 0.8 wt. %, and in some embodiments, fromabout 0.1 wt.% to about 0.5 wt. % of the anodizing solution. If desired,blends of acids may also be employed.

A current is passed through the anodizing solution to form thedielectric layer. The value of the formation voltage manages thethickness of the dielectric layer. For example, the power supply may beinitially set up at a galvanostatic mode until the required voltage isreached. Thereafter, the power supply may be switched to apotentiostatic mode to ensure that the desired dielectric thickness isformed over the entire surface of the anode. Of course, other knownmethods may also be employed, such as pulse or step potentiostaticmethods. The voltage at which anodic oxidation occurs typically rangesfrom about 4 to about 250 V, and in some embodiments, from about 9 toabout 200 V, and in some embodiments, from about 20 to about 150 V.During oxidation, the anodizing solution can be kept at an elevatedtemperature, such as about 30° C. or more, in some embodiments fromabout 40° C. to about 200° C., and in some embodiments, from about 50°C. to about 100° C. Anodic oxidation can also be done at ambienttemperature or lower. The resulting dielectric layer may be formed on asurface of the anode and within its pores.

The capacitor elements also contain a solid electrolyte that functionsas the cathode for the capacitor. A manganese dioxide solid electrolytemay, for instance, be formed by the pyrolytic decomposition of manganousnitrate (Mn(NO₃)₂). Such techniques are described, for instance, in U.S.Pat. No. 4,945,452 to Sturmer, et al., which is incorporated herein inits entirety by reference thereto for all purposes.

Alternatively, the solid electrolyte may be formed from one or moreconductive polymer layers. The conductive polymer(s) employed in suchlayers are typically π-conjugated and have electrical conductivity afteroxidation or reduction, such as an electrical conductivity of at leastabout 1 μS cm⁻¹ after oxidation. Examples of such π-conjugatedconductive polymers include, for instance, polyheterocycles (e.g.,polypyrroles, polythiophenes, polyanilines, etc.), polyacetylenes,poly-p-phenylenes, polyphenolates, and so forth. Particularly suitableconductive polymers are substituted polythiophenes having the followinggeneral structure:

wherein,

T is O or S;

D is an optionally substituted C₁ to C₅ alkylene radical (e.g.,methylene, ethylene, n-propylene, n-butylene, n-pentylene, etc.);

R₇ is a linear or branched, optionally substituted C₁ to C₁₈ alkylradical (e.g., methyl, ethyl, n- or iso-propyl, n-, iso-, sec- ortert-butyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl,1-ethylpropyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl,2,2-dimethylpropyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl,n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-hexadecyl,n-octadecyl, etc.); optionally substituted C₅ to C₁₂ cycloalkyl radical(e.g., cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononylcyclodecyl, etc.); optionally substituted C₆ to C₁₄ aryl radical (e.g.,phenyl, naphthyl, etc.); optionally substituted C₇ to C₁₈ aralkylradical (e.g., benzyl, o-, m-, p-tolyl, 2,3-, 2,4-, 2,5-, 2-6, 3-4-,3,5-xylyl, mesityl, etc.); optionally substituted C₁ to C₄ hydroxyalkylradical, or hydroxyl radical; and

q is an integer from 0 to 8, in some embodiments, from 0 to 2, and inone embodiment, 0; and

n is from 2 to 5,000, in some embodiments from 4 to 2,000, and in someembodiments, from 5 to 1,000. Example of substituents for the radicals“D” or “R₇” include, for instance, alkyl, cycloalkyl, aryl, aralkyl,alkoxy, halogen, ether, thioether, disulphide, sulfoxide, sulfone,sulfonate, amino, aldehyde, keto, carboxylic acid ester, carboxylicacid, carbonate, carboxylate, cyano, alkylsilane and alkoxysilanegroups, carboxylamide groups, and so forth.

Particularly suitable thiophene polymers are those in which “D” is anoptionally substituted C₂ to C₃ alkylene radical. For instance, thepolymer may be optionally substituted poly(3,4-ethylenedioxythiophene),which has the following general structure:

Methods for forming conductive polymers, such as described above, arewell known in the art. For instance, U.S. Pat. No. 6,987,663 to Merker,et al., which is incorporated herein in its entirety by referencethereto for all purposes, describes various techniques for formingsubstituted polythiophenes from a monomeric precursor. The monomericprecursor may, for instance, have the following structure:

wherein,

T, D, R₇, and q are defined above. Particularly suitable thiophenemonomers are those in which “D” is an optionally substituted C₂ to C₃alkylene radical. For instance, optionally substituted3,4-alkylenedioxythiophenes may be employed that have the generalstructure:

wherein, R₇ and q are as defined above. In one particular embodiment,“q” is 0. One commercially suitable example of 3,4-ethylenedioxthiopheneis available from Heraeus Clevios under the designation Clevios™ M.Other suitable monomers are also described in U.S. Pat. No. 5,111,327 toBlohm, et al. and U.S. Pat. No. 6,635,729 to Groenendaal, et al., whichare incorporated herein in their entirety by reference thereto for allpurposes. Derivatives of these monomers may also be employed that are,for example, dimers or trimers of the above monomers. Higher molecularderivatives, i.e., tetramers, pentamers, etc. of the monomers aresuitable for use in the present invention. The derivatives may be madeup of identical or different monomer units and used in pure form and ina mixture with one another and/or with the monomers. Oxidized or reducedforms of these precursors may also be employed.

The thiophene monomers are chemically polymerized in the presence of anoxidative catalyst. The oxidative catalyst typically includes atransition metal cation, such as iron(II), copper(II), chromium(VI),cerium(IV), manganese(IV), manganese(VII), ruthenium(III) cations, etc.A dopant may also be employed to provide excess charge to the conductivepolymer and stabilize the conductivity of the polymer. The dopanttypically includes an inorganic or organic anion, such as an ion of asulfonic acid. In certain embodiments, the oxidative catalyst employedin the precursor solution has both a catalytic and doping functionalityin that it includes a cation (e.g., transition metal) and anion (e.g.,sulfonic acid). For example, the oxidative catalyst may be a transitionmetal salt that includes iron(III) cations, such as iron(III) halides(e.g., FeCl₃) or iron(III) salts of other inorganic acids, such asFe(ClO₄)₃ or Fe₂ (SO₄)₃ and the iron(III) salts of organic acids andinorganic acids comprising organic radicals. Examples of iron (III)salts of inorganic acids with organic radicals include, for instance,iron(III) salts of sulfuric acid monoesters of C₁ to C₂₀ alkanols (e.g.,iron(III) salt of lauryl sulfate). Likewise, examples of iron(III) saltsof organic acids include, for instance, iron(III) salts of C₁ to C₂₀alkane sulfonic acids (e.g., methane, ethane, propane, butane, ordodecane sulfonic acid); iron (III) salts of aliphatic perfluorosulfonicacids (e.g., trifluoromethane sulfonic acid, perfluorobutane sulfonicacid, or perfluorooctane sulfonic acid); iron (III) salts of aliphaticC₁ to C₂₀ carboxylic acids (e.g., 2-ethylhexylcarboxylic acid); iron(III) salts of aliphatic perfluorocarboxylic acids (e.g.,trifluoroacetic acid or perfluorooctane acid); iron (III) salts ofaromatic sulfonic acids optionally substituted by C₁ to C₂₀ alkyl groups(e.g., benzene sulfonic acid, o-toluene sulfonic acid, p-toluenesulfonic acid, or dodecylbenzene sulfonic acid); iron (III) salts ofcycloalkane sulfonic acids (e.g., camphor sulfonic acid); and so forth.Mixtures of these above-mentioned iron(III) salts may also be used.Iron(III)-p-toluene sulfonate, iron(III)-o-toluene sulfonate, andmixtures thereof, are particularly suitable. One commercially suitableexample of iron(III)-p-toluene sulfonate is available from HeraeusClevios under the designation Clevios™ C.

Various methods may be utilized to form a conductive polymer layer. Inone embodiment, the oxidative catalyst and monomer are applied, eithersequentially or together, such that the polymerization reaction occursin situ on the part. Suitable application techniques may includescreen-printing, dipping, electrophoretic coating, and spraying, may beused to form a conductive polymer coating. As an example, the monomermay initially be mixed with the oxidative catalyst to form a precursorsolution. Once the mixture is formed, it may be applied to the part andthen allowed to polymerize so that the conductive coating is formed onthe surface. Alternatively, the oxidative catalyst and monomer may beapplied sequentially. In one embodiment, for example, the oxidativecatalyst is dissolved in an organic solvent (e.g., butanol) and thenapplied as a dipping solution. The part may then be dried to remove thesolvent therefrom. Thereafter, the part may be dipped into a solutioncontaining the monomer.

Polymerization is typically performed at temperatures of from about −10°C. to about 250° C., and in some embodiments, from about 0° C. to about200° C., depending on the oxidizing agent used and desired reactiontime. Suitable polymerization techniques, such as described above, maybe described in more detail in U.S. Pat. No. 7,515,396 to Biler. Stillother methods for applying such conductive coating(s) may be describedin U.S. Pat. Nos. 5,457,862 to Sakata, et al., 5,473,503 to Sakata, etal., 5,729,428 to Sakata, et al., and 5,812,367 to Kudoh, et al., whichare incorporated herein in their entirety by reference thereto for allpurposes.

In addition to in situ application, a conductive polymer layer may alsobe applied in the form of a dispersion of conductive polymer particles.Although their size may vary, it is typically desired that the particlespossess a small diameter to increase the surface area available foradhering to the anode part. For example, the particles may have anaverage diameter of from about 1 to about 500 nanometers, in someembodiments from about 5 to about 400 nanometers, and in someembodiments, from about 10 to about 300 nanometers. The D₉₀ value of theparticles (particles having a diameter of less than or equal to the D₉₀value constitute 90% of the total volume of all of the solid particles)may be about 15 micrometers or less, in some embodiments about 10micrometers or less, and in some embodiments, from about 1 nanometer toabout 8 micrometers. The diameter of the particles may be determinedusing known techniques, such as by ultracentrifuge, laser diffraction,etc.

The formation of the conductive polymers into a particulate form may beenhanced by using a separate counterion to counteract the positivecharge carried by the substituted polythiophene. In some cases, thepolymer may possess positive and negative charges in the structuralunit, with the positive charge being located on the main chain and thenegative charge optionally on the substituents of the radical “R”, suchas sulfonate or carboxylate groups. The positive charges of the mainchain may be partially or wholly saturated with the optionally presentanionic groups on the radicals “R.” Viewed overall, the polythiophenesmay, in these cases, be cationic, neutral or even anionic. Nevertheless,they are all regarded as cationic polythiophenes as the polythiophenemain chain has a positive charge.

The counterion may be a monomeric or polymeric anion. Polymeric anionscan, for example, be anions of polymeric carboxylic acids (e.g.,polyacrylic acids, polymethacrylic acid, polymaleic acids, etc.);polymeric sulfonic acids (e.g., polystyrene sulfonic acids (“PSS”),polyvinyl sulfonic acids, etc.); and so forth. The acids may also becopolymers, such as copolymers of vinyl carboxylic and vinyl sulfonicacids with other polymerizable monomers, such as acrylic acid esters andstyrene. Likewise, suitable monomeric anions include, for example,anions of C₁ to C₂₀ alkane sulfonic acids (e.g., dodecane sulfonicacid); aliphatic perfluorosulfonic acids (e.g., trifluoromethanesulfonic acid, perfluorobutane sulfonic acid or perfluorooctane sulfonicacid); aliphatic C₁ to C₂₀ carboxylic acids (e.g.,2-ethyl-hexylcarboxylic acid); aliphatic perfluorocarboxylic acids(e.g., trifluoroacetic acid or perfluorooctanoic acid); aromaticsulfonic acids optionally substituted by C₁ to C₂₀ alkyl groups (e.g.,benzene sulfonic acid, o-toluene sulfonic acid, p-toluene sulfonic acidor dodecylbenzene sulfonic acid); cycloalkane sulfonic acids (e.g.,camphor sulfonic acid or tetrafluoroborates, hexafluorophosphates,perchlorates, hexafluoroantimonates, hexafluoroarsenates orhexachloroantimonates); and so forth. Particularly suitablecounteranions are polymeric anions, such as a polymeric carboxylic orsulfonic acid (e.g., polystyrene sulfonic acid (“PSS”)). The molecularweight of such polymeric anions typically ranges from about 1,000 toabout 2,000,000, and in some embodiments, from about 2,000 to about500,000.

When employed, the weight ratio of such counterions to substitutedpolythiophenes in a given layer is typically from about 0.5:1 to about50:1, in some embodiments from about 1:1 to about 30:1, and in someembodiments, from about 2:1 to about 20:1. The weight of the substitutedpolythiophene referred to in the above-referenced weight ratios refersto the weighed-in portion of the monomers used, assuming that a completeconversion occurs during polymerization.

The dispersion may also contain one or more binders to further enhancethe adhesive nature of the polymeric layer and also increase thestability of the particles within the dispersion. The binders may beorganic in nature, such as polyvinyl alcohols, polyvinyl pyrrolidones,polyvinyl chlorides, polyvinyl acetates, polyvinyl butyrates,polyacrylic acid esters, polyacrylic acid amides, polymethacrylic acidesters, polymethacrylic acid amides, polyacrylonitriles, styrene/acrylicacid ester, vinyl acetate/acrylic acid ester and ethylene/vinyl acetatecopolymers, polybutadienes, polyisoprenes, polystyrenes, polyethers,polyesters, polycarbonates, polyurethanes, polyamides, polyimides,polysulfones, melamine formaldehyde resins, epoxide resins, siliconeresins or celluloses. Crosslinking agents may also be employed toenhance the adhesion capacity of the binders. Such crosslinking agentsmay include, for instance, melamine compounds, masked isocyanates orfunctional silanes, such as 3-glycidoxypropyltrialkoxysilane,tetraethoxysilane and tetraethoxysilane hydrolysate or crosslinkablepolymers, such as polyurethanes, polyacrylates or polyolefins, andsubsequent crosslinking. Other components may also be included withinthe dispersion as is known in the art, such as dispersion agents (e.g.,water), surface-active substances, etc.

If desired, one or more of the above-described application steps may berepeated until the desired thickness of the coating is achieved. In someembodiments, only a relatively thin layer of the coating is formed at atime. The total target thickness of the coating may generally varydepending on the desired properties of the capacitor. Typically, theresulting conductive polymer coating has a thickness of from about 0.2micrometers (“μm”) to about 50 μm, in some embodiments from about 0.5 μmto about 20 μm, and in some embodiments, from about 1 μm to about 5 μm.It should be understood that the thickness of the coating is notnecessarily the same at all locations on the part. Nevertheless, theaverage thickness of the coating on the substrate generally falls withinthe ranges noted above.

The conductive polymer layer may optionally be healed. Healing may occurafter each application of a conductive polymer layer or may occur afterthe application of the entire coating. In some embodiments, theconductive polymer can be healed by dipping the part into an electrolytesolution, and thereafter applying a constant voltage to the solutionuntil the current is reduced to a preselected level. If desired, suchhealing can be accomplished in multiple steps. For example, anelectrolyte solution can be a dilute solution of the monomer, thecatalyst, and dopant in an alcohol solvent (e.g., ethanol). The coatingmay also be washed if desired to remove various byproducts, excessreagents, and so forth.

If desired, the capacitor may also contain other layers as is known inthe art. For example, a protective coating may optionally be formedbetween the dielectric and solid electrolyte, such as one made of arelatively insulative resinous material (natural or synthetic). Suchmaterials may have a specific resistivity of greater than about 10 Ω/cm,in some embodiments greater than about 100, in some embodiments greaterthan about 1,000 Ω/cm, in some embodiments greater than about 1×10⁵Ω/cm, and in some embodiments, greater than about 1×10¹⁰ Ω/cm. Someresinous materials that may be utilized in the present inventioninclude, but are not limited to, polyurethane, polystyrene, esters ofunsaturated or saturated fatty acids (e.g., glycerides), and so forth.For instance, suitable esters of fatty acids include, but are notlimited to, esters of lauric acid, myristic acid, palmitic acid, stearicacid, eleostearic acid, oleic acid, linoleic acid, linolenic acid,aleuritic acid, shellolic acid, and so forth. These esters of fattyacids have been found particularly useful when used in relativelycomplex combinations to form a “drying oil”, which allows the resultingfilm to rapidly polymerize into a stable layer. Such drying oils mayinclude mono-, di-, and/or tri-glycerides, which have a glycerolbackbone with one, two, and three, respectively, fatty acyl residuesthat are esterified. For instance, some suitable drying oils that may beused include, but are not limited to, olive oil, linseed oil, castoroil, tung oil, soybean oil, and shellac. These and other protectivecoating materials are described in more detail U.S. Pat. No. 6,674,635to Fife, et al., which is incorporated herein in its entirety byreference thereto for all purposes.

The part may also be applied with a carbon layer (e.g., graphite) andsilver layer, respectively. The silver coating may, for instance, act asa solderable conductor, contact layer, and/or charge collector for thecapacitor and the carbon coating may limit contact of the silver coatingwith the solid electrolyte. Such coatings may cover some or all of thesolid electrolyte.

Generally speaking, the capacitor elements are substantially free ofresins that encapsulate the elements as are often employed inconventional solid electrolytic capacitors. Among other things, theencapsulation of the capacitor elements can lead to instability inextreme environments, i.e., high temperature (e.g., above about 175° C.)and/or high voltage (e.g., above about 35 volts).

II. Housing

As indicated above, the capacitor elements are hermetically sealedwithin a housing. Any of a variety of different materials may be used toform the housing, such as metals, plastics, ceramics, and so forth. Inone embodiment, for example, the housing includes one or more layers ofa metal, such as tantalum, niobium, aluminum, nickel, hafnium, titanium,copper, silver, steel (e.g., stainless), alloys thereof (e.g.,electrically conductive oxides), composites thereof (e.g., metal coatedwith electrically conductive oxide), and so forth. In anotherembodiment, the housing may include one or more layers of a ceramicmaterial, such as aluminum nitride, aluminum oxide, silicon oxide,magnesium oxide, calcium oxide, glass, etc., as well as combinationsthereof.

The housing may have any desired shape, such as cylindrical, D-shaped,rectangular, triangular, prismatic, etc. Referring to FIGS. 1-3, forexample, one embodiment of a capacitor assembly 100 is shown thatcontains a housing 122 and juxtaposed capacitor elements 120 a and 120b. In this particular embodiment, the housing 122 is generallyrectangular. Typically, the housing and the capacitor elements have thesame or similar shape so that the elements can be readily accommodatedwithin the interior cavity. In the illustrated embodiment, for example,housing 122 and the capacitor elements 120 a and 120 b have a generallyrectangular shape.

The manner in which the capacitor elements are arranged within thehousing is generally selected to reduce the likelihood that they becomedelaminated upon being subjected to vibrational forces. In theillustrated embodiment, for example, the capacitor elements 120 a and120 b are juxtaposed so that a side surface 403 a of the capacitorelement 120 a is positioned adjacent to and faces a side surface 403 bof the capacitor element 120 b, and so that a side surface 405 a of thecapacitor element 120 a faces away from a side surface 405 b of thecapacitor element 120 b. In addition to being juxtaposed adjacent toeach other, the capacitor elements 120 a and 120 b are also aligned sothat they have major surfaces (e.g., surface having largest area)oriented in a horizontal configuration. For example, the capacitorelement 120 a and 120 b each have a major surface 181 and 183 thatextends in a plane defined by their width (−x direction) and length (−ydirection). In this manner, the major surfaces of the capacitor elementsare generally coplanar and extend in the same direction (e.g., −ydirection) as the length of the housing 122 to which it is connected.This provides a variety of benefits, among which include the ability toincrease the contact surface area between the capacitor elements and thehousing, which help them better withstand vibrational forces to whichthey are exposed. Of course, it should also be understood that thecapacitor elements may be arranged so that their major surfaces are notcoplanar, but perpendicular to each other in a certain direction, suchas the −z direction or the −x direction. The capacitor elements also doneed not to extend in the same direction.

If desired, the capacitor assembly of the present invention may exhibita relatively high volumetric efficiency. To facilitate such highefficiency, the capacitor elements typically occupy a substantialportion of the volume of an interior cavity of the housing. For example,the capacitor elements may occupy about 30 vol. % or more, in someembodiments about 50 vol. % or more, in some embodiments about 60 vol. %or more, in some embodiments about 70 vol. % or more, in someembodiments from about 80 vol. % to about 98 vol. %, and in someembodiments, from about 85 vol. % to 97 vol. % of the interior cavity ofthe housing. To this end, the difference between certain dimensions ofthe capacitor elements and those of the interior cavity defined by thehousing are typically relatively small.

Referring to FIG. 3, for example, the capacitor element 120 a may have alength (excluding the length of the anode lead 6) that is relativelysimilar to the length of an interior cavity 126 defined by the housing122. For example, the ratio of the length of the anode to the length ofthe interior cavity ranges from about 0.40 to 1.00, in some embodimentsfrom about 0.50 to about 0.99, in some embodiments from about 0.60 toabout 0.99, and in some embodiments, from about 0.70 to about 0.98. Thecapacitor element 120 a may have a length of from about 5 to about 10millimeters, and the interior cavity 126 may have a length of from about6 to about 15 millimeters. Similarly, the ratio of the height of thecapacitor element 120 a (in the −z direction) to the height of theinterior cavity 126 may range from about 0.40 to 1.00, in someembodiments from about 0.50 to about 0.99, in some embodiments fromabout 0.60 to about 0.99, and in some embodiments, from about 0.70 toabout 0.98. For example, the height of the capacitor element 120 a maybe from about 0.5 to about 2 millimeters and the height of the interiorcavity 126 may be from about 0.7 to about 6 millimeters.

Although by no means required, the capacitor elements may be attached tothe housing in such a manner that a common anode termination and cathodetermination are formed external to the housing for subsequentintegration into a circuit. The particular configuration of theterminations may depend on the intended application. In one embodiment,for example, the capacitor assembly may be formed so that it is surfacemountable, and yet still mechanically robust. For example, the anodelead of a capacitor element may be electrically connected to external,surface mountable anode and cathode terminations (e.g., pads, sheets,plates, frames, etc.). Such terminations may extend through the housingto connect with the capacitor. The thickness or height of theterminations is generally selected to minimize the thickness of thecapacitor assembly. For instance, the thickness of the terminations mayrange from about 0.05 to about 1 millimeter, in some embodiments fromabout 0.05 to about 0.5 millimeters, and from about 0.1 to about 0.2millimeters. If desired, the surface of the terminations may beelectroplated with nickel, silver, gold, tin, etc. as is known in theart to ensure that the final part is mountable to the circuit board. Inone particular embodiment, the termination(s) are deposited with nickeland silver flashes, respectively, and the mounting surface is alsoplated with a tin solder layer. In another embodiment, thetermination(s) are deposited with thin outer metal layers (e.g., gold)onto a base metal layer (e.g., copper alloy) to further increaseconductivity.

In certain embodiments, connective members may be employed within theinterior cavity of the housing to facilitate connection to theterminations in a mechanically stable manner. For example, referringagain to FIG. 1, the capacitor assembly 100 may include connectionmembers 162 that are formed from a first portion 167 and a secondportion 165. The connection members 162 may be formed from conductivematerials similar to the external terminations. The first portion 167and second portion 165 may be integral or separate pieces that areconnected together, either directly or via an additional conductiveelement (e.g., metal). In the illustrated embodiment, the second portion165 is provided in a plane that is generally parallel to a lateraldirection in which the lead 6 of each capacitor element extends (e.g.,−y direction). The first portion 167 is “upstanding” in the sense thatit is provided in a plane that is generally perpendicular the lateraldirection in which the lead 6 extends. In this manner, the first portion167 can limit movement of the lead 6 in the horizontal direction toenhance surface contact and mechanical stability during use. If desired,an insulative material 7 (e.g. Teflon™ washer) may be employed aroundthe lead 6 of the capacitor elements.

The first portion 167 may possess a mounting region (not shown) that isconnected to the anode lead 6 of a respective capacitor element 120 a or120 b. The region may have a “U-shape” for further enhancing surfacecontact and mechanical stability of the lead 6. Connection of the regionto the lead 6 may be accomplished using any of a variety of knowntechniques, such as welding, laser welding, conductive adhesives, etc.In one particular embodiment, for example, the region is laser welded tothe anode lead 6. Regardless of the technique chosen, however, the firstportion 167 can hold the anode lead 6 in substantial horizontalalignment to further enhance the dimensional stability of the capacitorassembly 100.

Referring again to FIG. 1, one embodiment of the present invention isshown in which the connective member 162 and respective capacitorelement 120 a or 120 b are connected to the housing 122 through anodeand cathode terminations 127 and 129, respectively. The anodetermination 127 contains a first region 127 a that is positioned withinthe housing 122 and electrically connected to the connection member 162and a second region 127 b that is positioned external to the housing 122and provides a mounting surface 201. Likewise, the cathode termination129 contains a first region 129 a that is positioned within the housing122 and electrically connected to the solid electrolyte of the capacitorelement 120 and a second region 129 b that is positioned external to thehousing 122 and provides a mounting surface 203. It should be understoodthat the entire portion of such regions need not be positioned within orexternal to the housing.

In the illustrated embodiment, a conductive trace 127 c extends in anouter wall 123 of the housing to connect the first region 127 a andsecond region 127 b. Similarly, a conductive trace 129 c extends in theouter wall 123 of the housing to connect the first region 127 a andsecond region 127 b. The conductive traces and/or regions of theterminations may be separate or integral. In addition to extendingthrough the outer wall of the housing, the traces may also be positionedat other locations, such as external to the outer wall. Of course, thepresent invention is by no means limited to the use of conductive tracesfor forming the desired terminations.

Regardless of the particular configuration employed, connection of theterminations 127 and 129 to the capacitor elements 120 a and 120 b maybe made using any known technique, such as welding, laser welding,conductive adhesives, etc. In one particular embodiment, for example, aconductive adhesive 131 is used to connect the second portion 165 of theconnection member 162 to the anode termination 127. Likewise, aconductive adhesive 133 is used to connect the cathode of the capacitorelement 120 to the cathode termination 129. The conductive adhesives maybe formed from conductive metal particles contained with a resincomposition. The metal particles may be silver, copper, gold, platinum,nickel, zinc, bismuth, etc. The resin composition may include athermoset resin (e.g., epoxy resin), curing agent (e.g., acidanhydride), and coupling agent (e.g., silane coupling agents). Suitableconductive adhesives are described in U.S. Patent ApplicationPublication No. 2006/0038304 to Osako, et al., which is incorporatedherein in its entirety by reference thereto for all purposes.

Optionally, a polymeric restraint may also be disposed in contact withone or more surfaces of the capacitor elements, such as the rearsurface, front surface, upper surface, lower surface, side surface(s),or any combination thereof. The polymeric restraint can reduce thelikelihood of delamination by the capacitor element from the housing. Inthis regard, the polymeric restraint may possesses a certain degree ofstrength that allows it to retain the capacitor element in a relativelyfixed positioned even when it is subjected to vibrational forces, yet isnot so strong that it cracks. For example, the restraint may possess atensile strength of from about 1 to about 150 Megapascals (“MPa”), insome embodiments from about 2 to about 100 MPa, in some embodiments fromabout 10 to about 80 MPa, and in some embodiments, from about 20 toabout 70 MPa, measured at a temperature of about 25° C. It is normallydesired that the restraint is not electrically conductive.

Although any of a variety of materials may be employed that have thedesired strength properties noted above, curable thermosetting resinshave been found to be particularly suitable for use in the presentinvention. Examples of such resins include, for instance, epoxy resins,polyimides, melamine resins, urea-formaldehyde resins, polyurethanes,silicone polymers, phenolic resins, etc. In certain embodiments, forexample, the restraint may employ one or more polyorganosiloxanes.Silicon-bonded organic groups used in these polymers may containmonovalent hydrocarbon and/or monovalent halogenated hydrocarbon groups.Such monovalent groups typically have from 1 to about 20 carbon atoms,preferably from 1 to 10 carbon atoms, and are exemplified by, but notlimited to, alkyl (e.g., methyl, ethyl, propyl, pentyl, octyl, undecyl,and octadecyl); cycloalkyl (e.g., cyclohexyl); alkenyl (e.g., vinyl,allyl, butenyl, and hexenyl); aryl (e.g., phenyl, tolyl, xylyl, benzyl,and 2-phenylethyl); and halogenated hydrocarbon groups (e.g.,3,3,3-trifluoropropyl, 3-chloropropyl, and dichlorophenyl). Typically,at least 50%, and more preferably at least 80%, of the organic groupsare methyl. Examples of such methylpolysiloxanes may include, forinstance, polydimethylsiloxane (“PDMS”), polymethylhydrogensiloxane,etc. Still other suitable methyl polysiloxanes may includedimethyldiphenylpolysiloxane, dimethyl/methylphenylpolysiloxane,polymethylphenylsiloxane, methylphenyl/dimethylsiloxane, vinyldimethylterminated polydimethylsiloxane, vinylmethyl/dimethylpolysiloxane,vinyldimethyl terminated vinylmethyl/dimethylpolysiloxane, divinylmethylterminated polydimethylsiloxane, vinylphenylmethyl terminatedpolydimethylsiloxane, dimethylhydro terminated polydimethylsiloxane,methylhydro/dimethylpolysiloxane, methylhydro terminatedmethyloctylpolysiloxane, methylhydro/phenylmethyl polysiloxane, etc.

The organopolysiloxane may also contain one more pendant and/or terminalpolar functional groups, such as hydroxyl, epoxy, carboxyl, amino,alkoxy, methacrylic, or mercapto groups, which impart some degree ofhydrophilicity to the polymer. For example, the organopolysiloxane maycontain at least one hydroxy group, and optionally an average of atleast two silicon-bonded hydroxy groups (silanol groups) per molecule.Examples of such organopolysiloxanes include, for instance,dihydroxypolydimethylsiloxane,hydroxy-trimethylsiloxypolydimethylsiloxane, etc. Other examples ofhydroxyl-modified organopolysiloxanes are described in U.S. PatentApplication Publication No. 2003/0105207 to Klever, et al., which isincorporated herein in its entirety by reference thereto for allpurposes. Alkoxy-modified organopolysiloxanes may also be employed, suchas dimethoxypolydimethylsiloxane,methoxy-trimethylsiloxypolydimethylsiloxane,diethoxypolydimethylsiloxane,ethoxy-trimethylsiloxy-polydimethylsiloxane, etc. Still other suitableorganopolysiloxanes are those modified with at least one aminofunctional group. Examples of such amino-functional polysiloxanesinclude, for instance, diamino-functional polydimethylsiloxanes. Variousother suitable polar functional groups for organopolysiloxanes are alsodescribed in U.S. Patent Application Publication No. 2010/00234517 toPlantenberg, et al., which is incorporated herein in its entirety byreference thereto for all purposes.

Epoxy resins are also particularly suitable for use as the polymericrestraint. Examples of suitable epoxy resins include, for instance,glycidyl ether type epoxy resins, such as bisphenol A type epoxy resins,bisphenol F type epoxy resins, phenol novolac type epoxy resins,orthocresol novolac type epoxy resins, brominated epoxy resins andbiphenyl type epoxy resins, cyclic aliphatic epoxy resins, glycidylester type epoxy resins, glycidylamine type epoxy resins, cresol novolactype epoxy resins, naphthalene type epoxy resins, phenol aralkyl typeepoxy resins, cyclopentadiene type epoxy resins, heterocyclic epoxyresins, etc. Still other suitable conductive adhesive resins may also bedescribed in U.S. Patent Application Publication No. 2006/0038304 toOsako, et al. and U.S. Pat. No. 7,554,793 to Chacko, which areincorporated herein in their entirety by reference thereto for allpurposes.

If desired, curing agents may also be employed in the polymericrestraint to help promote curing. The curing agents typically constitutefrom about 0.1 to about 20 wt. % of the restraint. Exemplary curingagents include, for instance, amines, peroxides, anhydrides, phenolcompounds, silanes, acid anhydride compounds and combinations thereof.Specific examples of suitable curing agents are dicyandiamide, 1-(2cyanoethyl)2-ethyl-4-methylimidazole, 1-benzyl 2-methylimidazole, ethylcyano propyl imidazole, 2-methylimidazole, 2-phenylimidazole,2-ethyl-4-methylimidazole, 2-undecylimidazole,1-cyanoethyl-2-methylimidazole,2,4-dicyano-6,2-methylimidazolyl-(1)-ethyl-s-triazine, and2,4-dicyano-6,2-undecylimidazolyl-(1)-ethyl-s-triazine, imidazoliumsalts (such as 1-cyanoethyl-2-undecylimidazolium trimellitate,2-methylimidazolium isocyanurate, 2-ethyl-4-methylimidazoliumtetraphenylborate, and 2-ethyl-1,4-dimethylimidazoliumtetraphenylborate, etc. Still other useful curing agents includephosphine compounds, such as tributylphosphine, triphenylphosphine,tris(dimethoxyphenyl)phosphine, tris(hydroxypropyl)phosphine, andtris(cyanoethyl)phsphine; phosphonium salts, such astetraphenylphosphonium-tetraphenylborate,methyltributylphosphonium-tetraphenylborate, andmethyltricyanoethylphosphonium tetraphenylborate); amines, such as2,4,6-tris(dimethylaminomethyl)phenol, benzylmethylamine,tetramethylbutylguanidine, N-methylpiperazine, and2-dimethylamino-1-pyrroline; ammonium salts, such as triethylammoniumtetraphenylborate; diazabicyclo compounds, such as1,5-diazabicyclo[5,4,0]-7-undecene, 1,5-diazabicyclo[4,3,0]-5-nonene,and 1,4-diazabicyclo[2,2,2]-octane; salts of diazabicyclo compounds suchas tetraphenylborate, phenol salt, phenolnovolac salt, and2-ethylhexanoic acid salt; and so forth.

Still other additives may also be employed, such as photoinitiators,viscosity modifiers, suspension aiding agents, pigments, stress reducingagents, coupling agents (e.g., silane coupling agents), nonconductivefillers (e.g., clay, silica, alumina, etc.), stabilizers, etc. Suitablephotoinitiators may include, for instance, benzoin, benzoin methylether, benzoin ethyl ether, benzoin n-propyl ether, benzoin isobutylether, 2,2 dihydroxy-2-phenylacetophenone,2,2-dimethoxy-2-phenylacetophenone 2,2-diethoxy-2-phenylacetophenone,2,2-diethoxyacetophenone, benzophenone, 4,4-bisdialylaminobenzophenone,4-dimethylaminobenzoic acid, alkyl 4-dimethylaminobenzoate,2-ethylanthraquinone, xanthone, thioxanthone, 2-cholorothioxanthone,etc. When employed, such additives typically constitute from about 0.1to about 20 wt. % of the total composition.

Referring again to FIGS. 1-3, for instance, one embodiment is shown inwhich a polymeric restraint 197 is disposed in contact with an uppersurface 181 and rear surface 177 of each capacitor element 120 a and 120b. While a single restraint is shown for each element, it should beunderstood that separate restraints may be employed to accomplish thesame function. In fact, more generally, any number of polymericrestraints may be employed to contact any desired surface of thecapacitor elements. When multiple restraints are employed, they may bein contact with each other or remain physically separated. For example,in one embodiment, a second polymeric restraint (not shown) may beemployed that contacts the upper surface 181 and front surface 179 ofthe capacitor element 120 a. The first polymeric restraint 197 and thesecond polymeric restraint (not shown) may or may not be in contact witheach other. In yet another embodiment, a polymeric restraint may alsocontact a lower surface 183 and/or side surface 403 a and 405 a of thecapacitor element 120 a, either in conjunction with or in lieu of othersurfaces.

Regardless of how it is applied, it is typically desired that thepolymeric restraint is also in contact with at least one surface of thehousing to help further mechanically stabilize the capacitor elementagainst possible delamination. For example, the restraint may be incontact with an interior surface of one or more sidewall(s), outer wall,lid, etc. In FIGS. 1-3, for example, the polymeric restraints 197 are incontact with interior surfaces 107 and 109 of the housing 122. While incontact with the housing, it is nevertheless desired that at least aportion of the cavity defined by the housing remains unoccupied to allowfor the inert gas to flow through the cavity and limit contact of thesolid electrolyte with oxygen. For example, at least about 5% of thecavity volume typically remains unoccupied by the capacitor element andpolymer restraint, and in some embodiments, from about 10% to about 50%of the cavity volume.

Once connected in the desired manner, the resulting package ishermetically sealed. Referring again to FIGS. 1-3, for instance, thehousing 122 may also include a lid 125 that is placed on an uppersurface of side walls 124 and 525 after the capacitor elements 120 a and120 b are positioned within the housing 122. The lid 125 may be formedfrom a ceramic, metal (e.g., iron, copper, nickel, cobalt, etc., as wellas alloys thereof), plastic, and so forth. If desired, a sealing member187 may be disposed between the lid 125 and the side walls 124 and 525to help provide a good seal. In one embodiment, for example, the sealingmember may include a glass-to-metal seal, Kovar® ring (GoodfellowCamridge, Ltd.), etc. The height of the side walls 124 and 525 isgenerally such that the lid 125 does not contact any surface of thecapacitor elements 120 a and 120 b so that it is not contaminated. Theoptional polymeric restraint 197 may or may not contact the lid 125.When placed in the desired position, the lid 125 is hermetically sealedto the sidewalls 124 and 525 using known techniques, such as welding(e.g., resistance welding, laser welding, etc.), soldering, etc.

Hermetic sealing typically occurs in the presence of a gaseousatmosphere that contains at least one inert gas so as to inhibitoxidation of the solid electrolyte during use. The inert gas mayinclude, for instance, nitrogen, helium, argon, xenon, neon, krypton,radon, and so forth, as well as mixtures thereof. Typically, inert gasesconstitute the majority of the atmosphere within the housing, such asfrom about 50 wt. % to 100 wt. %, in some embodiments from about 75 wt.% to 100 wt. %, and in some embodiments, from about 90 wt. % to about 99wt. % of the atmosphere. If desired, a relatively small amount ofnon-inert gases may also be employed, such as carbon dioxide, oxygen,water vapor, etc. In such cases, however, the non-inert gases typicallyconstitute 15 wt. % or less, in some embodiments 10 wt. % or less, insome embodiments about 5 wt. % or less, in some embodiments about 1 wt.% or less, and in some embodiments, from about 0.01 wt. % to about 1 wt.% of the atmosphere within the housing. For example, the moisturecontent (expressed in terms of relatively humidity) may be about 10% orless, in some embodiments about 5% or less, in some embodiments about 1%or less, and in some embodiments, from about 0.01 to about 5%.

It should be understood that the embodiments described are onlyexemplary, and that various other configurations may be employed in thepresent invention. For example, the embodiments discussed above areconnected to the anode and cathode terminations using similar connectivemembers. However, this is by no means required, and any of a variety ofdifferent connection mechanisms may be employed for each differentcapacitor element. Likewise, different terminations may also beemployed. In one embodiment, for example, terminal pins may be employedrather than surface-mountable external terminations. Such pins mayoptionally extend through an outer wall of the housing.

As a result of the present invention, the capacitor assembly may exhibitexcellent electrical properties even when exposed to high temperatureand high voltage environments. For example, the capacitor assembly mayexhibit a relatively high “breakdown voltage” (voltage at which thecapacitor fails), such as about 35 volts or more, in some embodimentsabout 50 volts or more, in some embodiments about 60 volts or more, andin some embodiments, from about 60 volts to about 100 volts, such asdetermined by increasing the applied voltage in increments of 3 voltsuntil the leakage current reaches 1 mA. Likewise, the capacitor may alsobe able to withstand relatively high surge currents, which is alsocommon in high voltage applications. The peak surge current may, forexample, about 2 times the rated voltage or more, such as range fromabout 40 Amps or more, in some embodiments about 60 Amps or more, and insome embodiments, and in some embodiments, from about 120 Amps to about250 Amps.

The capacitance may likewise be about 1 milliFarad per square centimeter(“mF/cm²”) or more, in some embodiments about 2 mF/cm² or more, in someembodiments from about 5 to about 50 mF/cm², and in some embodiments,from about 8 to about 20 mF/cm². The capacitance may be determined at anoperating frequency of 120 Hz and a temperature of 25° C. In addition,the capacitor assembly can also exhibit a relatively high percentage ofits wet capacitance, which enables it to have only a small capacitanceloss and/or fluctuation in the presence of atmosphere humidity. Thisperformance characteristic is quantified by the “dry to wet capacitancepercentage”, which is determined by the equation:

Dry to Wet Capacitance=(1−([Wet−Dry]/Wet))×100

The capacitor assembly of the present invention, for instance, mayexhibit a dry to wet capacitance percentage of about 80% or more, insome embodiments about 85% or more, in some embodiments about 90% ormore, and in some embodiments, from about 92% to 100%.

The capacitor assembly may also have an equivalence series resistance(“ESR”) of less than about 50 ohms, in some embodiments less than about25 ohms, in some embodiments from about 0.01 to about 10 ohms, and insome embodiments, from about 0.05 to about 5 ohms, measured at anoperating frequency of 100 kHz. In addition, the leakage current, whichgenerally refers to the current flowing from one conductor to anadjacent conductor through an insulator, can be maintained at relativelylow levels. For example, the numerical value of the normalized leakagecurrent of a capacitor of the present invention is, in some embodiments,less than about 1 μA/μF*V, in some embodiments less than about 0.5μA/μF*V, and in some embodiments, less than about 0.1 μA/μF*V, where μAis microamps and μF*V is the product of the capacitance and the ratedvoltage.

The electrical properties, such as described above, may even bemaintained after aging for a substantial amount of time at hightemperatures. For example, the values may be maintained for about 100hours or more, in some embodiments from about 300 hours to about 3000hours, and in some embodiments, from about 400 hours to about 2500 hours(e.g., 500 hours, 600 hours, 700 hours, 800 hours, 900 hours, 1000hours, 1100 hours, 1200 hours, or 2000 hours) at temperatures rangingfrom about 100° C. to about 250° C., and, in some embodiments from about100° C. to about 225° C., and in some embodiments, from about 100° C. toabout 225° C. (e.g., 100° C., 125° C., 150° C., 175° C., or 200° C.).

The present invention may be better understood by reference to thefollowing examples.

Test Procedures Equivalent Series Resistance (ESR)

Equivalence series resistance may be measured using a Keithley 3330Precision LCZ meter with Kelvin Leads 2.2 volt DC bias and a 0.5 voltpeak to peak sinusoidal signal. The operating frequency was 100 kHz andthe temperature was 23° C.±2° C.

Capacitance

The capacitance was measured using a Keithley 3330 Precision LCZ meterwith Kelvin Leads with 2.2 volt DC bias and a 0.5 volt peak to peaksinusoidal signal. The operating frequency was 120 Hz and thetemperature was 23° C.±2° C.

Vibration Testing:

The part was subjected to the entire frequency range of 10 Hz to 2.000Hz and then returned to 10 Hz and reversed in 20 minutes. This cycle wasperformed 12 times in each of the 3 directions (a total of 36 times) sothat motion was applied for a total period of approximately 12 hours.The vibration amplitude was 3.0 mm from 10 Hz to the higher cross-overfrequency and then 20 g acceleration to 2.000 Hz. Ten (10) samples ofthe capacitor were soldered onto a testing plate and put into thistesting.

Example 1

A tantalum anode (4.80 mm×5.25 mm×2.60 mm) was anodized at 30V in aliquid electrolyte to 150 μF. A conductive polymer coating was thenformed by dipping the entire anode into apoly(3,4-ethylenedioxythiophene) (“PEDT”) dispersion (Clevios™ K, solidscontent of 1.1%). The part was then dried at 125° C. for 20 minutes.This process was repeated 10 times. Thereafter, the part was dipped at aspeed of 0.1 mm/s into a PEDT dispersion (solids content of 2.8%) sothat the dispersion reached the shoulder of the part as shown in FIG. 3.The part was left in the dispersion for 10 seconds, dried at 125° C. for30 minutes, and then cooled down to room temperature. This process wasrepeated 5 times. The part was then coated with graphite and silver. Acopper-based leadframe material was used to finish the assembly process.A single cathode connective member was attached to the lower surface ofthe capacitor element using a silver adhesive. The tantalum wire of thecapacitor element was then laser welded to an anode connective member.

Two capacitor elements were formed in the manner described above, andthen the anode and cathode connective members of the respectiveleadframes were glued to a gold cathode termination and welded to a goldanode termination located inside a ceramic housing having a length of11.00 mm, a width of 12.50 mm, and a thickness of 5.40 mm. The housinghad gold plated solder pads on the bottom inside part of ceramichousing. The adhesive employed for the cathode connection was a silverpaste (EPO-Tek E3035) and the adhesive was applied only between theleadframe portions and gold plated solder pad. The welding employed forthe anode connection was a resistance welding and the energy of 190 Wwas applied between the leadframe portions and ceramic housing goldplated solder pad during 90 ms. The assembly was then loaded in aconvection reflow oven to solder the paste. After reflow, a polymericrestraint material (Dow Corning® 736 heat resistant sealant) was appliedover the top of the anode and cathode portions of the capacitor elementsand was dried at 165° C. for 1.5 hours. After that, a Kovar® lid havinga length of 9.95 mm, a width of 4.95 mm, and a thickness of 0.10 mm wasplaced over the top of the container, closely on the seal ring of theceramic housing (Kovar® ring having a thickness of 0.30 mm) so thatthere was no direct contact between the interior surface of the lid andthe exterior surface of the attached capacitor. The resulting assemblywas placed into a welding chamber and purged with nitrogen gas for 120minutes before seam welding between the seal ring and the lid wasperformed. No additional burn-in or healing was performed after the seamwelding. Multiple parts (50) were made in this manner.

Example 2

A tantalum anode (4.80 mm×10.50 mm×2.60 mm) was anodized at 30V in aliquid electrolyte to 150 μF. A conductive polymer coating was thenformed by dipping the entire anode into apoly(3,4-ethylenedioxythiophene) (“PEDT”) dispersion (Clevios™ K, solidscontent of 1.1%). The part was then dried at 125° C. for 20 minutes.This process was repeated 10 times. Thereafter, the part was dipped at aspeed of 0.1 mm/s into a PEDT dispersion (solids content of 2.8%) sothat the dispersion reached the shoulder. The part was left in thedispersion for 10 seconds, dried at 125° C. for 30 minutes, and thencooled down to room temperature. This process was repeated 5 times. Thepart was then coated with graphite and silver. Multiple parts (50) werethen formed from the capacitor elements in the same manner describedabove.

The parts of Examples 1 and 2 were then tested for electricalperformance (i.e., capacitance (“CAP”) and equivalent series resistance(“ESR”)), before and after “vibration testing” as described above attemperature 25° C. The median results are shown below.

Before Vibration After Vibration Testing Testing Sample CAP (μF) ESR(mohms) CAP (μF) ESR (mohms) Example 1 270 57 263 71 Example 2 274 65Open circuit

As indicated, the capacitor assemblies of Example 2, which contained asingle large anode (length of 10.5 mm), were less stable under extremeconditions than the smaller, multi-anode assemblies (length of 5.25 mm)employed in Example 1.

These and other modifications and variations of the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention. Inaddition, it should be understood that aspects of the variousembodiments may be interchanged both in whole or in part.

Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention so further described in such appended claims.

1. A capacitor assembly comprising: a housing that defines an interiorcavity having a gaseous atmosphere that contains an inert gas; a firstcapacitor element juxtaposed adjacent to a second capacitor element,wherein the first and second capacitor elements are positioned in theinterior cavity and connected to the housing, each of the capacitorelements comprising an anode formed from an anodically oxidized,sintered porous body and a solid electrolyte overlying the anode,wherein each capacitor element further comprises an anode lead thatextends in a lateral direction from the porous body of the anode,wherein the lead is positioned within the interior cavity of thehousing; an anode termination that is in electrical connection with theanode lead of each of the capacitor elements; and a cathode terminationthat is in electrical connection with the solid electrolyte of each ofthe capacitor elements.
 2. The capacitor assembly of claim 1, wherein aside surface of the first capacitor element is positioned adjacent toand faces a side surface of the second capacitor element.
 3. Thecapacitor assembly of claim 1, wherein the first capacitor element has afirst major surface and the second capacitor element has a second majorsurface, wherein the first major surface and the second major surfaceare connected to the housing.
 4. The capacitor assembly of claim 3,wherein the first major surface and the second major surface aregenerally coplanar.
 5. The capacitor assembly of claim 1, furthercomprising a connective member that is electrically connected to atleast one of the capacitor elements, wherein the connective membercontains a first portion that is positioned generally perpendicular tothe lateral direction of the anode lead and connected thereto.
 6. Thecapacitor assembly of claim 5, wherein the connective member furthercontains a second portion that is generally parallel to the lateraldirection in which the anode lead extends.
 7. The capacitor assembly ofclaim 6, wherein the second portion is positioned within the housing. 8.The capacitor assembly of claim 6, wherein the first capacitor elementhas a first major surface that is connected to the housing via theconnective member.
 9. The capacitor assembly of claim 1, wherein theporous body is formed from tantalum or niobium oxide.
 10. The capacitorassembly of claim 1, wherein the solid electrolyte includes a conductivepolymer.
 11. The capacitor assembly of claim 10, wherein the conductivepolymer is in the form of a particle dispersion.
 12. The capacitorassembly of claim 1, wherein the solid electrolyte includes manganesedioxide.
 13. The capacitor assembly of claim 1, wherein capacitorelements occupy about 30 vol. % or more of the interior cavity.
 14. Thecapacitor assembly of claim 1, wherein inert gases constitute from about50 wt. % to 100 wt. % of the gaseous atmosphere.
 15. The capacitorassembly of claim 1, further comprising a polymeric restraintspositioned adjacent to and in contact with a surface of at least one ofthe capacitor elements and a surface of the housing.
 16. The capacitorassembly of claim 1, wherein from 2 to 4 capacitor elements arepositioned in the interior cavity of the housing.